A light guide element includes a hollow housing defining a cavity and a reflective film. The housing includes a front wall with an opening, a closed rear wall opposite to the front wall, and four sidewalls interconnected between the front wall and the rear wall. One of the sidewalls defines a number of light output holes. The opening and the light output holes communicate with the cavity. The reflective film is formed on the entirely inner side surfaces of the housing in the cavity. Light from the opening is repeatedly reflected by the reflective film in the cavity and finally exits the housing through the light input holes.